This invention relates, in general, to a diffraction grating, and more particularly, to a tunable diffraction grating.
Information may be transmitted through optical wavelengths in the visible and near visible region. The amount of information which may be transmitted through optical wavelengths may be increased by multiplexing several beams of light, each of a different wavelength and modulated such that it alone is transmitting a large amount of information.
These wavelengths of light, or signal, is usually transmitted through an optical fiber. Each individual wavelength of light then must be separated in order to receive and process the information transmitted on it. A diffraction grating is suitable for this purpose. Semiconductor devices, such as photodetectors, are used to further process the wavelength of light.
A diffraction grating of the prior art consists of a glass, quartz, or plastic material having peaks and valleys or rows having a fixed spacing. The material is transparent at the wavelength of interest. An optical fiber is positioned such that the light traverses the diffraction grating. The spacing between the rows or the valleys between the peaks are positioned such that the wavelength of interest is diffracted along the grating. This means that the spacing or width of the valleys must be fixed along a predetermined section of the grating. The spacing or width of the valleys can be different in different sections of the diffraction grating such that different wavelengths of light diffract at different sections along the grating. Each of the wavelengths may then be further processed at particular locations along the diffraction grating.
If these diffraction gratings are integrated along with semiconductor integrated circuits, it would be desirable for the diffraction grating to be easily integratable and for it to be as small as possible. In order to monitor a large amount of information, either multiple diffraction gratings having fixed spacing or a large grating having variable spacing is necessary. It is also necessary to have multiple photodetectors, one for each grating or one for each wavelength of light to be monitored along a grating having variable spacing. It would be desirable to be able to monitor large amounts of information on one small diffraction grating.
Another method of separating wavelengths of light is with the use of Fabri-Perrot interferometers with piezoelectric drives. The disadvantage of these structures is that they are complicated, delicate, and expensive, and thus will not be further described. It would be desirable to provide a diffraction grating that can monitor various wavelengths of light which is inexpensive and not complicated.
Accordingly, it is an object of the present invention to provide a diffraction grating which can monitor large amounts of information by being able to tune the diffraction grating to diffract different wavelengths of light.
Another object of the present invention is to provide a tunable diffraction grating which may be easily integrated onto a semiconductor device.
A further object of the present invention is to provide a tunable diffraction grating which is inexpensive to fabricate.
Yet another object of the present invention is to provide a way to change the spacing of the rows of a diffraction grating.